1. Field of the Invention
This invention relates to smoke-generating pyrotechnic compositions.
A smoke-generating composition typically comprises the following constituents:
a sublimable organic dye which generates a colored smoke through its change of state,
an oxidizing system
a reducing system serving as binder between the oxidizing agent, the dye and catalysts which are optionally present, and which controls the speed of the reaction during its combustion,
additives for example hardeners and plasticizers for the binder, wetting agent to assist the kneading of the composition, cooling agent and stabilising agent.
These constituents are generally kneaded together and the paste thus obtained is then cast in a mold so that after hardening the composition can be readily stored and handled.
The production of sufficient colored smoke will depend for a given dye, on the nature of the binder, the oxidizing agent and the additives; the choice of these additives affects the following parameters:
the minimum temperature at which the oxidizing system is operative,
the maximum temperature at which the binder is stable,
the maximum temperature at which the dye is stable,
the possible reaction between the dye and the binder which is liable to inhibit the polymerization of the binder.
2. Description of the prior art
Numerous smoke generating pyrotechnic compositions have been proposed as a result of researches undertaken principally to improve the length of time during which smoke is emitted. Recent improvements have been contributed by U.K. Pat. No. 2,004,536 in which there is described a castable smoke generating composition comprising a synthetic resin combustible at low temperature by reaction with an oxidizing system constituted by the combination of potassium or sodium chlorate and guanidine nitrate. It was noted that the temperature for combustion or decomposition of this castable smoke generating composition was in the range of about 190.degree. to 300.degree. C. With combustion taking place in this way, there is obtained at this temperature a rapid sublimation of the organic dye used, which allows the retention of a particularly large portion for use at any moment in its combustion. It is also possible to use the organic dyes currently manufactured commercially without their undergoing occlusion by the residues resulting from the combustion of the composition. For more detail, reference may be made to the text of this patent.